texts: Is there a threshold on distance/size for a tidal locking?

texts:
I know that some systems tend to tidal locking (such as earth-moon), which occurs basically because the difference in the gravitational pull on one side is significantly different from the pull on the opposite side. (There's a lot of great answers here.) But what can be considered a significant different?
In other words, is there a threshold on distance or size in order for systems to tend to tidal lock?

Thanks!


texts: Could celestial coordinates be encoded into three-word combinations?

texts:
I came across this cool tool which encodes geographic coordinates into 3 dictionary words - table.lamp.chair - for example. You can see their map here https://map.what3words.com/. It divides the world into a grid of 57 trillion 3mx3m squares and each one is assigned with one of these three-word addresses.
It made me curious as to whether this sort of thing could work for communicating the locations of stars.

It would be pretty simple to assign unique three-word addresses to stars in stellar databases. What would be even more powerful is if we could encode celestial coordinates into three-word addresses, and create an interactive "what3words" space map. But would this be at all useful?

The finite surface area of the earth allows us to create the grid of 57 trillion squares. Can we work with the infinite nature of the celestial sphere to create something similar?


texts: How much time does it take for a meteor (shooting star) to touch the ground after its combustion?

texts: I know that meteors that We see as shooting stars travel tens of thousands of kilometers per hour and are tiny as a grain of sand, but after hitting the atmosphere and burn I suppose that its ashes would touch the ground at some point. How long does it take? Can it be measured or observed?


texts: Why doesn't the sun pull the moon away from earth?

texts: If the suns gravitational pull is strong enough to hold much larger masses in place (all the planets) and at much greater distances (all planets further away from the sun then earth) why does it not pull the moon away from earth?


texts: How to read Babylonians' tablet that were used to track Jupiter's movements?

texts:
There is a science news article on how Babylonians used geometry to track Jupiter’s movements.

Here is an image of cuneiform tablet which shows Jupiter's movements.

From a layman's point of view, it looks like someone engraved gibberish on a tablet. How do we even know it was used to track Jupiter's movements.

Can anyone translate this? Thanks.


texts: Refraction by Saturn's atmosphere - how dense is it here?

texts:
This tweet from CassiniSaturn shows an image of Saturn's rings being optically distorted by the dense atmosphere. It is explained more fully on this page and is available here.

The refraction is visible because at at least some depth, the density and path length is sufficient to bend the light significantly while the density and composition is still sufficiently transparent.

Roughly speaking, what is the density where this is taking place? Is it rarefied compared to earth but simply a very very long path length, or is this happening at a density far larger than Earth's surface atmosphere? How large is this refraction -  like 0.1 degrees or 10 degrees? I can't picture the actual geometry very well.

This one may be a bit of a judgement call, unless this image happens to be further documented somewhere.

above: cropped portion of the NASA's Cassini image from here


texts:
So a black hole is this large, sphere-blob shaped fluid thing that distorts space and time, making a weird hole in space(even after 5 years, I still don't exactly get what a black hole is exactly and where the mass goes when it eats xD).

So, let's say, we make a huge antimatter(opposite charge, same mass as matter) star and send it into the black hole. What would happen? The antimatter would annihilate with the matter made black hole, or is it wrong to assume a black hole is made of matter?(I assume not much would happen if the antimatter can't react with the matter, because the black hole would probably get its original charge messed up.)

What about if we created a huge exotic matter(same charge, opposite mass) star and sent it into a black hole? Would the repulsive force successfully destroy a black hole? According to Kurzgesagt and several articles cited by them, exotic matter is able to keep a wormhole stable, so wouldn't it be able to annihilate the black hole or something? Or have I made a misunderstanding?


texts: What is the distance between the solar systems towards the center of galaxy?

texts: The distance from our Solar System to the nearest is roughly 260,000 AU. I am wondering what is the minimum distance between two Solar Systems. Since the center of our galaxy is supposed to be more dense than the spiral on which our Solar System is situated, I am guessing that the distances between adjacent Solar Systems would be smaller. Please give quantitative figures and references to peer-reviewed journals if possible.


texts: What's the difference between the apparent horizon and event horizon of a black hole?

texts: The Wikipedia page for apparent horizon is pretty sketchy and requires some GR knowledge. Is there any simple definition?


texts: Can ground based telescopes use a starshade in space?

texts:
1) Could a starshade in orbit be used by ground based telescopes? If so, what kind of orbit should it have?

2) Could the same starshade be used by two different space telescopes, or does the positioning make it impractical?


texts: According to this video stars at end of time  and many others on fate of universe they all agree on one  thing that stars will eventually convert  all the hydrogen into heavier elements and eventually there will be no light , i understand the documentaries are over simplified but is it really the case that universe had/has finite amount of hydrogen to start with and there is no known process that recycling hydrogen back into universe


texts: How many stars are between Milky way and Andromeda?

texts:
Are there some stars between those two galaxies? In photos is only black.

And if so, how many we could find there?


texts: What could have made a satellite appear to move side to side while near the horizon?

texts:
Yesterday while coming out of a restaurant my wife and I noticed what appeared be a satellite passing quite high in the sky. Based on the location, time, and brightness this appears to have been a passing of the GEOS 3 Rocket. What made this unusual is that when it got low (perhaps 25-30 degrees off the horizon) it suddenly appeared to dart side to side (over 15 degree sweeps) multiple times over perhaps a second, while continuing its general western trend, before vanishing.

Since this all happened rather quickly I had to estimate the distances after the fact using my hands and what few reference points were available. It is certainly possible that it was lower in the sky than my estimate as that is always a tricky part to judge. I'm quite certain of the sweep distance but an answer that could explain a smaller sweep could still be very useful.

What could cause a satellite to appear to move side to side in this fashion?


texts: Does Jupiter rotate at the same speed at every depth?

texts: Jupiter rotates in less than 10 hours. Its rotation is differential, with the upper layers of the atmosphere spinning a bit faster at the equator than at higher latitudes. Do the inner layers of Jupiter rotate at the same (angular) speed as the outmost layers of the atmosphere?


texts:
A long time ago I read a very interesting way of studying the sun's internal structure via sound waves. This new field of study, probability already known here, is called helioseismology.

How much can we learn from gas giants by "listening" to sound waves?

Somewhat tangent to the question: Does this extend to all other kind of giants such as hot Jupiter, ice giants, etc...?


texts: How small could an orbital system be in our solar system?

texts:
Answers to How does the Sun's gravity have so much force and pull on the solar system? How does it scale? Newton's law of gravity scales on orbits so that we can theorize very small orbits with very small masses.
Could two hydrogen molecules orbit one another or would external gravity prevent them from having a stable orbit? We know there are quite small orbital systems in our own asteroid belt, but is there a practical limit to how small an orbital system (with the little orbital system also orbiting the Sun) can be in terms of total mass of the orbital system?


texts: Quantum Mechanics after the detection of Gravitational Waves

texts:
Of course everyone knows by now of the detection of Gravitational waves

But, since General Relativity and Quantum Mechanics don't get along, can we say now that this detection proves that Quantum Mechanics doesn't actually apply and that General Relativity did prevail?

Another question: how can we identify the ripple's origin (let's say whether it's a result of the big bang or another big event)?

EDIT 16-2-2016

I was reading an article today and I thought I'd share it here; It's basically saying that without a third detector we can't triangulate the signal.
Some scientists tried ways to observe the light of the event directly after the observations of the wave but they couldn't detect the merger simply because it's too far away or too faint to be observed with our current technology.


texts: What are the typical emissions of Jupiter's Aurorae?

texts:
I'm looking for some solid measurements of the full range of emissions from the Aurorae on Jupiter. I've found partial sets of data in the past which are most easily summarized here. As you can see, this set of data is missing several ranges of emissions. The missing ranges I'm most interested in are from .18μm-.385μm, and 1μm-3μm. Graphs are greatly appreciated so I can integrate certain wavelengths myself, as well as different data sets which separate the power of emissions into more specific categories such as UVA/UVB/UVC.
The holy grail of answering this question would be a graph similar to a black body radiation graph with the x-axis being wavelengths in μm and the Y axis being Spectral Radiance as seen here:

Source


texts: How to calculate the temperature of a star

texts:
I need a way to calculate the effective temperature (surface temperature) of a star for a stellar model. I need something in the form Te=....

I have:

Radius in m
mass in kg
the composition of particles (eg H 90%, He 8% etc)
the combined stored thermal energy of the body in J

Constants (any really but I'm using these for now):

G=gravity constant=6.67408E-011
k=kbolzmann=1.3806485279E-023
s=sbolzmann=5,67036713E-008
PI=pi ~3.14...

Example of the sun:

mp=average mass of a particle=1,7E-027
M=total mass of the body=2E30
r=radius of the body=700000000

I'm using this equation to estimate the core temperature :

(G*mp*M)/(r*(3/2)*k)

which nets 15653011 for the sun which is close enough given that that is the only star core temperature known (afaik).

I'm using this to estimate the luminosity L:

4*PI*(r^2)*s*(Te^4)

which results in an error of ~1-5%  with 90% of my sample stars which is close enough. For the sun this results in 3,95120075975041E+026 W which is only 2,7% off.

The problem is I need Te for the 2nd formula which I don't have in my scenario.

Due to the formula for L being dependent on the surface temperature to the power of 4 this value has to be relatively precise.

Assumptions of my model:

uniform distribution of particles: so every slice of the body has the same composition as the entire body.
perfect sphere: every body is a perfect sphere, no handling for elliptic bodies needed.

My sample values (first line is the sun with a core temp of 15000000):

     emitted energy Surface temp    radius       mass
     (in Lsun)      (in K)          (in m)       (in Msun)
     1              5800            700000000    1
     8700000        53000           25200000000  265
     6300000        50100           23100000000  110
     2900000        42000           23660000000  132
     2000000        44000           16800000000  80
     1260000        13500           140000000000 45
     57500          3600            618100000000 12.4
     78             5700            6440000000   2.56
     78.5           4940            8540000000   2.69
     15100          7350            51100000000  9.7
     1.519          5790            858900000    1.1
     0.5            5260            605500000    0.907
     370000         3690            994000000000 19.2
     123000         33000           7560000000   56
     2200000        52500           12600000000  130
     200000         10000           151900000000 22
     446000         19000           43330000000  42.3
     25.4           9940            1197700000   2.02

Errors in luminosity to actual value (the maximum error is about 100% which I can live with since it might just be inaccurate measurements for the sample stars)

2.74%
6.71%
-1.13%
11.29%
-2.00%
-4.27%
106.76%
3.99%
2.51%
-6.50%
1.12%
4.00%
-8.27%
2.10%
1.57%
113.75%
1.64%
2.15%


texts: Is Bode's Law just a series of remarkable coincidences,or would it hold good for other solar systems where the star is similar to our sun?


texts: The Vela pulsar is a neutron star from a supernova that exploded 10,000 years ago. It spins 11 times a second. The Crab Nebula along with the central Crab Pulsar formed 1000 years ago. This pulsar spins 30 times a second. If there's a famous Crab Pulsar with a nebula, is there a Vela Nebula in which the Vela Pulsar is within?


texts: Are we still in the Solar Maximus stage? Will this winter 2013/14 be a good aurora-viewing season?

texts: I remember reading in 2011 that 2013/2014 would be the peak of the current solar maximus, but I want to confirm whether that is still ongoing.  Will the upcoming winter season be a good time to see the Northern Lights?


texts: Can the paper narrowing Solar System's barycentre to within 100m help find Planet Nine?

texts:
I've just read this recent news article, Astronomers Have Located The Centre of The Solar System to Within 100 Metres, reporting on a paper[1] that claims narrowing the Solar System barycentre to within 100 meters, just outside the sun, and I wonder, could this result help prove or disprove the hypothesis of a massive Planet Nine as proposed by Batygin and Brown[2] in 2016?
I imagine that any unknown mass concentration would change the barycentre and generate a error, and if we could measure this error, it should be possible to pinpoint the position of said mass concentration. Can we just use probe tracking data from the Voyagers or Pioneers to see if their hyperbolic trajectories match the barycentre reported in the paper, for example?
[1]. Vallisneri, M., et al. “Modeling the Uncertainties of Solar System Ephemerides for Robust Gravitational-wave Searches with Pulsar-timing Arrays”. The Astrophysical Journal, vol. 893, no 2, abril de 2020, p. 112. DOI.org (Crossref), doi:10.3847/1538-4357/ab7b67.
[2]. Batygin, Konstantin, e Michael E. Brown. “Evidence for a Distant Giant Planet in the Solar System”. The Astronomical Journal, vol. 151, no 2, janeiro de 2016, p. 22. arXiv.org, doi:10.3847/0004-6256/151/2/22.


texts: Do astronomers have any reason to believe that the Small Magellanic Cloud (SMC) collided with the Milky Way? If so, how do astronomers think about the concept of collision? Would a collision only happen when stars in one arbitrarily defined galactic area cross over into another? How would these areas in space be defined?


texts: What is the mnemonic reason behind b being galactic latitude? (in the Galactic Coordinates frame)

texts:
I'm not sure if this is a question that has been posted before, and I'm also not sure if the answer is really mnemonic. If that's the case, I'd like to understand why we assigned $b$ to latitude anyways, so my brain can remember it more easily.
Thanks!


texts:
I’m new to this site after googling “do satellites travel in groups”. I read the discussion with posts from 2016 and 2019 and their descriptions did match what we (my wife and I) just witnessed minutes ago.
 I live in Dalhart Texas. We saw the event within 1 hour of sunset. We witnessed at least 15 objects but there could have been many more before we first saw them.
 As the previous comments stated, the objects we saw were also moving NW to SE. No blinking lights, no tell tale red or green lights. Solid light just like countless satellites I have seen before. Same steady pace but all in synchronized direction and speed. Not all were evenly spaced though. As they traveled SE they all slowly dimmed and disappeared all the same point in the sky. This must be the point at which the suns rays no longer reached the “satellites”. These objects appeared in the same relation to the moon as mentioned in a previous comment on this thread.
 I’m a bit suprised there are so few related sightings posted here. If these “satellites” orbit the earth then there must be countless sightings.
Thank you for your time


texts: Explaining the Drake Equation on a smaller scale

texts:
So me and my friend were planning a video to explain the Drake Equation (within a time limit of 5 minutes), and we needed some help. This video is aimed at explaining the concept to an age group between 13-18 years, and having gone through loads of articles, we felt that a lot of the common audience would not be able to comprehend the concept.

So our question was, can we take the Drake Equation and try to explain it with maybe a real life example and on a smaller scale? It is an incredibly interesting equation and we felt like doing a good job of explaining it to a common teenager.

Thanks!


texts: Where would an object fly to if it were to leave the gravitational field of Earth? And would it stop somewhere? What would happen to it?

texts: My 3,5 year old son is asking :-) He can take answers for a 15 yo I think. Many thanks for your help!


texts:
While out viewing the Perseid shower last night (8/11/20), we saw an interesting object that I'm trying to identify. We're in the vicinity of Portland, Oregon. It appeared to be traveling west->east and would be almost invisible to the naked eye for 10 or so seconds, then flare up to be the brightest object in the sky for ~2 seconds. We saw two passes (or two separate objects) over the course of an hour, the first was a bit to the south (say 1 o'clock), the second was farther north (11 o'clock), it might have been the same object.
I was thinking it might be a Starlink satellite, but I would have expected to see more than just one. Also, I wouldn't think they would be that bright, being as small as they are.
I've not seen anything like that before, and it surely would have been noticeable in my past stargazing.
Anyone know what it might be?


texts: Why do the solar system planets go rock-gas-ice instead of rock-ice-gas when moving away from the sun?

texts:
The sun and the solar wind seem to do a good job of fractionating lighter materials to the outer solar system and leaving heavier materials in the inner solar system. So we end up with rocky/metallic planets in the inner solar system and the gas giants and ice giants in the outer solar system.
But why are the gas giants (Jupiter and Saturn composed mainly of Hydrogen and Helium - the lightest materials) closer to the sun than the ice giants (Uranus and Neptune composed of water, ammonia, methane, etc.)?


texts: Using parallax to find distance to the moon

texts:
I want to use the parallax method (from scratch) to find the distance between the earth and the moon. To get a significant parallax, I need to choose a large baseline. I live in India and my friend in the US and so the baseline will be about $13,000$ Km. That's quite a large so I suppose I would get a significant parallax.
What I don't think of, is taking of angle measurement?

How can I measure the angle $\alpha$?


texts: Can the Moon provide momentum to an object in Earth's orbit? Gravity Assisted Boost

texts:
Can a satellite maintain an equatorial orbit around Earth near the Moon's orbit to receive partial gravitational boosts by gaining momentum as the satellite passes though the Moon's gravity well?

I'm not asking about hanging out in the Lagrange points, but passing between the L2 point and the Moon or the Moon and Earth aligned, in a Moon assisted orbit.


texts: Is it possible to observe if there is traces of life on an exoplanet?

texts: We can observe exoplanets, but is it possible with today's technology to observe if there is life as we know it on an exoplanet? What do you look for when doing this kind of observation?


texts: Why is the cloud around Eta Carinae shaped the way it is?

texts:
According to (german) wikipedia, Eta Carinae has a cloud shaped like two cones with the points at the poles of the star as well as a disk around the equator. These matter clouds are mostly or only condensed stellar wind from Eta Carinae.

In my understanding, to create the dual-cone chape, the stellar wind provding the matter originates at the poles and this gives the dual cone shape (Ok?).

Why the poles? Stellar wind would, I guess, be mostly stellar matter so hot it reaches escape velocity, further pushed by the radiation. This should be isotropic. I can only guess that maybe Eta Carina has a magnetic field shaped similarly to earth with a north and south pole, nearer the equator the stellar wind is perpendicular to the field lines so the flightpaths of the charged particles are bent back inward. Near the poles the flightpaths and field lines are mostly paralell, so the magnetic field does not really act on the stellar wind. I included this guesswork on my part so you know where to start.

ETA: Turns out my guessing about stellar wind was wrong or mostly wrong, the cloud appears to be mostly shaped by eruptions in recentish history. But the question why they are shaped that way still stands.


texts: If a photon were 1 Planck length away from the event horizon of a blackhole, would it be able to escape the blackhole's gravitational pull?

texts:
I understand that one could theoretically replace the sun with a blackhole without affecting the orbits of the planets. This leads me to believe that a blackhole isn't a "cosmic vacuum cleaner" so much as it is a concentration of mass that has the strongest gravitational field known.

Intuitively, this must mean that there is a threshold beyond which escaping the blackhole's gravity becomes impossible even at light speed, which is the event horizon. Since a Planck length is the smallest unit known at which quantum gravitational effects become apparent, would it be reasonable to assume that a photon that is one Planck length away from the event horizon of a blackhole can escape its gravitational pull?


texts: Is the boulder on the peak of Tycho Crater the core of the impactor, or is it a random rock?

texts:
There's a strikingly visible boulder sitting right at the top of the peak complex in the center of Tycho Crater on the Moon.
Is it just a coincidence that this gigantic, bright rock is sitting dead center of the peak complex or is it a known piece of the original impactor that caused the wider crater? Does this remarkable rock have a name?
Image source

On 10 June 2011 the LRO spacecraft slewed 65° to the west, allowing the LROC NACs to capture this dramatic sunrise view of Tycho crater. A very popular target with amateur astronomers, Tycho is located at 43.37°S, 348.68°E, and is ~82 km (51 miles) in diameter. The summit of the central peak is 2 km (6562 ft) above the crater floor, and the crater floor is about 4700 m (15,420 ft) below the rim. Many "clasts" ranging in size from 10 meters to 100s of meters are exposed in the central peak slopes. Were these distinctive outcrops formed as a result of crushing and deformation of the target rock as the peak grew? Or do they represent preexisting rock layers that were brought intact to the surface? Imagine future geologists carefully making their way across these steep slopes, sampling a diversity of rocks brought up from depth. Tycho's features are so steep and sharp because the crater is young by lunar standards, only about 110 million years old. Over time, micrometeorites, and not so micro meteorites, will grind and erode these steep slopes into smooth mountains. For a preview of what Tycho's central peak may look like in a few billion years, visit Bhabha crater.
This is a version with about one fourth the linear pixel density of the original NASA full size image.

Original sources 1, 2  Credit: NASA / GSFC / Arizona State University


texts: Do stars made by universe getting smaller or larger in mass?

texts: Do stars made by universe getting smaller or larger in mass compared to stars made 180 million years after the Big Bang? If they are getting smaller, is this due to the fact that the universe is expanding and the interstellar mass that made stars is getting less denser?


texts: When did astronomy first discover that the stars are bigger than the moon?

texts:
We take it for granted these days that the stars are unimaginably bigger than the planets and the moons. But when you look at the sky, it does not appear this way.

The moon looks bigger and brighter than the stars. This leads me to wonder when astronomy first discovered the relative size of the stars.

Did people believe that the moon was bigger than the stars for a long time?
If so, where was this believed, and up until when?
What discoveries or observations led people to conclude that the stars are larger?


texts: What is the average time between a nebula formation and a neutron star?

texts:
I have a star project, and I couldn't find anything on the amount of time it takes from nebula to neutron star.

How long does it take, from a nebula, to form a neutron star?


texts: Has a “white hole” theory been advanced to explain anomalous star formation in Sagittarius A?

texts:
In 2008, the European Southern Observatory reported, upon the end of a 16-year study described here http://www.eso.org/public/usa/news/eso0846/, that the 28 stars nearest the very large black hole in Sagittarius A included 22 in varied orbits compared to a "swarm of bees", and six (all slightly farther from the BH) in a disc of very fast orbits. As the stars were "too young" to have migrated far, and as the tidal forces in black holes had apparently been felt to leave star formation in that region unlikely, further research was planned. I'm asking whether there might have been any results, given the torsion-based cosmology which pairs black holes with white ones and is most concisely described at arXiv.org > https://arxiv.org/abs/1510.08834.

The spin of smaller celestial bodies may affect the spin of the larger systems of which they're a part to an extremely great extent, according to a version of inflationary cosmology developed by physicist Nikodem Poplawski since 2009. The simplest statement of his cosmology is at https://arxiv.org/pdf/1007.0587.pdf, but, in spite of its title as an "alternative" to cosmological inflation, it actually describes a version of that theory, as pointed out in the Wikipedia article "Inflation": Poplawski's version uses an extension of Einstein's General Relativity that's usually referred to as the Einstein-Cartan-Sciama-Kibble (ECSK) theory of gravity, and was developed, partly in consultation between Einstein and the French mathematician Cartan, to incorporate particulate spin (the rotation of subatomic particles) into relativity, since GR had been formulated several years before such spin was discovered.

Partly because ECSK made an assumption that fermions (loosely describable as "matter particles") have a spatial extent (tiny, but about 37 times the Planck length) that's incompatible with a renormalization technique useful in quantum mechanics (which generally requires all subatomic particles to be pointlike), and perhaps partly because its application to cosmology allows a universe that's eternal to the past and to the future rather than one that's eternal only to the future, the ECSK theory has not been widely utilized in cosmology until recently, when physicists exasperated with the failure to discover any specialized subatomic particle that would cause inflation began turning to it. As you can see on p.7 in the piece I've linked you to, Poplawski's torsion-based cosmology may be falsified if there's no evidence for any prevalent direction of rotation, whereas inflationary cosmology that's based on a field of hypothesized "inflaton" particles cannot be falsified at all, leading to many recent objections to it by theoreticians.

I'd also like to know (if possible) whether the direction of the orbits of the stars concerned is the same as the direction of rotation of the super-massive BH itself, assuming that the latter was not inferred from the former: This would help me to assess the plausibility of this BH cosmology, as one of its leading proponents (Nikodem Poplawski) feels the arrow of time to derive from the direction of matter's passage across the event horizons of BHs, and has also felt the torsion-based theory to be falsifiable by the lack of a prevalent direction of rotation in the universe. (These are details to me, but might appear in whatever conversations or observations might contain the answer to my question.)


texts: Why has Saturn stopped contracting gravitationally?

texts:
The following text is from here:

The Jovian planets get their heat from the Sun and from their
interiors. Jupiter creates a lot of internal heat and releases this
heat by emitting thermal radiation. In fact, Jupiter creates so much
internal heat that it emits almost twice as much energy as it receives
from the Sun. The only reasonable explanation is that Jupiter is still
slowly contracting, almost as though it has not quite finished
forming.
Saturn and Neptune also appear to be emitting more energy than they
receive from the Sun. While we are certain Saturn is not still
contracting, it seems clear that Neptune is still contracting. Uranus
is the only jovian planet not emitting excess internal energy.

It make sense that the gas giants were formed from the force of gravity i.e. clouds of gas and dust particles contracted under their own weight, eventually becoming planetary bodies with solid core and gaseous atmospheres. For bodies whose bulk is mostly gas, it will contract towards its center and during such process, it will releases stored gravitational energy which will eventually convert into heat energy. Saturn is also a gaseous planet with rich gaseous atmosphere, so in theory, it should also contract under its own weight towards the center. So, why is it considered to have stopped contracting?
It is written here that Saturn has a different process for this internal heat formation because astronomers believe that unlike Jupiter, Saturn's formation process is complete and so, the heat energy is due to the falling of helium from clouds. Now, luminosity of planet (total power emitted by a spherical body) comes from the release of potential energy due to the gravitational contraction.
$${U = -\frac{GM^2}{R}}$$
$${L = \frac{dU}{dt} = \frac{GM^2}{R^2} \frac{dR}{dt}}$$
$${\frac{dR}{dt} = \frac{LR^2}{GM^2}}$$
Since, all the terms has non-zero value, there should be a non-zero value for the differential, even for Saturn implying that Saturn should contract with time. So, why astronomers believe Saturn's formation process to be complete (implying no further gravitational contraction)?
Related on physics.SE: What keeps a gas giant from falling in on itself?


texts: What are some challenging astrophysics problems for which we have data available?

texts:
I am a Computer Science student, and I would like to pursue a PhD in the same area, by applying artificial intelligence techniques to astrophysics. Not being an astrophysicist, however, I was curious about the main challenges in the field of astrophysics, and about the existence of numerical data related to them.
The goal would be to use deep learning techniques in fields where they have not been used so far, in order to obtain better results or to find something new. In particular, I find black holes fascinating, and a research in that field may be something very interesting (also, I think there is a lot to discover in that field).
Thank you in advance for your time!


texts:
The Wikipedia article on tides shows a diagram with a tidal bulge both towards the Moon and on the antipodal point (the Sun isn't included in the diagram). Surely that's wrong - what would cause the antipodal bulge?

Image courtesy of Wikipedia user Jhbdel under the Creative Commons Attribution-Share Alike 3.0 Unported license.


texts: Why do neutron stars collide instead of just revolving around each other like planets revolve around the Sun?

texts:
We know about events like two neutron star colliding and resulting in a black hole, also collision of black holes, and collision of galaxies. But we never see a satellite such as a moon colliding with a planet, or a planet colliding with a star, or an artificial satellite colliding with Earth.

Can't such celestial bodies (like black holes or neutron stars) remain revolving each other? What makes them collide? Is anything other than gravity responsible for this?


texts: Betelgeuse in false colors, is this common?

texts:
First, take the original Betelgeuse image from ALMA and remove red and green channels. Then boost the blue channel luminosity by x10 to x20 and a lot of detail pops out.

This is the resulting image that can be reproduced from the original.

If you zoom into the picture you'll notice tiny concentric "ripples". Blue shifted light denotes high energy particles (as opposed to red shift).

My hypothesis (I'm not an astonomer!) is that we are seeing background radiation, while the star itself obstructs the background. The ripples would then indicate gravitational bending as those heavy particles cross the super-extended corona of the star.

Is there an accepted hypothesis about these artifacts?

EDIT:

The inner ring of pixel-mess around the black spot is out of gamut and thus "invalid data". The ripples are inside the corona and, finally, the outer parts of the image are relatively uninfluenced background radiation from other objects. There are NO ARTIFACTS on the R and G channels.

This image shows what I mean by "ripples":

As a counter-argument to myself I show this more recent picture taken by SPHERE with similar artifacts. Maybe I should conclude that the high-level structure is real while the low-level structures are artifacts caused by the measuring instrument itself hitting its sensibility levels.

PS: I posted this question also on reddit.

EDIT: blue channel histogram

This is how to see the blue channel color information. I use Krita which is by no means a scientific tool but its immediate usage helps.

Download the image from the ESO source link above (it's the "Full size original" 91.6MB TIFF image).

Then, in Krita, go to "Filter > Adjust > Color Adjustment curves...". On the channel drop-down select "B" and observe the following picture:

I have highlighted with RED the interesting zone. On the background you'll notice there is a histogram and that color information is only present to the far left between the bars. All other intensities (maybe byte value 10 and above?) do not occur in the image.

  To the far right there is a barely visible population of "byte value 255 pixels", those are the out-of-gamut pixels.

To see those pixels drag the upper-right corner knob to the left so that the curve is steep from 0 to 255 between the two red bars I've shown. This will magnify intensity by a factor of 10 or 20 and map very dim pixels to brighter blue.

The uploaded image (second link above) is the resulting image of this process. There is NO EXACT SPOT I'm talking about. It is an aura all around the black blob in the middle.


texts: Two lights roughly 5 minutes apart about as bright as Mars or maybe Saturn

texts: I'm in the Minneapolis/St. Paul area and around 9:30 on August 4th 2017 I saw a bright light that got dimmer moving from the tree line to the east up and to my left fairly slowly, and steadily getting dimmer. There were no flashing lights like an airplane. Around 5-10 minutes later I saw another light exactly like the first in nearly the same place going the same direction, they both faded and disappeared. I grew up in the north and have spent many nights out in hay fields staring at the sky but sadly I have never really studied astronomy and my guess at brightness is based on Google images. My first guess would have been a satellite but seeing two on the same path makes me think otherwise. Thoughts?


texts:
When an exocomet passes by our Sun in a trajectory that leads it to establish a Solar Orbit what eventually happens to it?
In addition to its original inertia and vector being altered what are the longer term affects that occur?


texts: As I was reading about the heliocentric model, a question came up: How was Nicolaus Copernicus able to figure out that the sun is at the center of the solar system, and that all planets orbit around it, even though the telescope had not been invented yet? During his time the geocentric model was the standard.


texts: Is it possible to move a planet out of its orbit? At least a lighter planet?

texts:
As observed by many researches our sun will be exhausted in the distant future. So does anyone think that driving our planet (or any planet) closer to the sun for more light and heat is a solution for life to survive on earth? Or would moving it out of the sun's gravitational field and taking it to some other solar system with a healthy star be better, possibly with some kind of thrusting mechanism that we may invent in future?

I am aware of the sun's gravity and the mass of the earth.


texts: Are planets more likely to have dense materials at their cores?

texts: When planets are forming, does the densest material sink the core and the less dense material "float" on top? What I'm asking is that are the more dense materials more likely to appear in the core rather than the surface. I'm also wondering, can a planet have an iron surface and still have rock beneath the surface in its crust and core?


texts: Could the Earth use gravitational lensing / bending of light to see it's own bottom?

texts:
Specifically, I have often wondered whether gravitational lensing might be able to (theoretically) be used in order to see light reflecting off the Earth that has zoomed off into space and been bent by one object after another until it comes full circle back to Earth again. Given the distance the light would have travelled, could we not use this technique to peer back through time at our own planet?

Is it reasonable that this could happen given the size of the universe and the mass and distribution of objects within it?
Given the restraints above, would be be able to estimate how far back in time we are looking?
Given the above, how bright would something have to be in order for its light to travel this distance and still be detectable?


texts: How to calculate what is the best date and latitude to observe a certain object in space?

texts: What is the mathematical formula used to do that? Is there a website/app that does the calculation for me?


texts: What is an Ideal apparent field of view for viewing planets through a zoom eyepiece?

texts: I was reading the specs of a few zoom eyepieces, and in every eyepiece, there is a term called 'apparent field of view'. I looked up and searched about it and figured out that if you divide this by the magnification caused by the eyepiece, you get the real field of view which is basically the diameter of the circle visible in the telescope. But one thing that I was unable to find that was what would be a good field of view for viewing planets through a zoom eyepiece, so this is my question.


texts: Units of angle in comoving transverse distance calculation

texts: For two objects at a redshift $z$, I know that the proper distance between them is given by $\delta \theta d_M(z)$, where $d_M(z)$ is the transverse comoving distance. What are the units of the angle out front? I know that $d_M$ has units of Mpc, but should the $\delta \theta$ be in degrees, radians, etc? And why is that the case?


texts:
I am having a slight disagreement with my professor.

We can measure the mass of a distant star cluster from:
A.Its color
B.Its radius
C.Its metallicity
D.Smearing of lines in its total spectrum

My thinking was:
Law of Conservation of Energy

Kinetic Energy = Gravitational force

1/2*m*v^2 =  G* m*M/r

v = sqrt(2GM/r)

So it is dependant on both velocity and radius.
Answer choice D would give you the velocity but I responded with answer choice B, radius.
After talking it over with my professor, she responded with:

If we think about it conceptually, the dominant parameter is the velocity.  In other words, you can get a meaningful estimate of the cluster mass from the velocity dispersion without knowing the radius (because all clusters are the "same" size), but not vice versa.
So I'd say it still seems pretty clear that the best answer is the velocities.

Is she right or is the question worded poorly?


texts: Can we get the gas compositions from a gas planets?

texts: Is it possible to get some gases like hydrogen from gas planets (Saturn, Jupiter,  Uranus or Neptune)?


texts: Should this photo of the sun's surface actually be white?

texts:
If I'm told correctly (eg. What Color is the Sun?) that the sun is actually white, should the photo on that page actually be white too? Is it just doctored to meet peoples expectations?:

Likewise for all the red photo's in a Google image search for "The Sun's surface".


texts: Why different specifications for telescopes and binoculars?

texts:
Sorry for the noob question but I don't seem to be able to find the answer on the internet.

I've been looking through some telescopes and binoculars and noticed that shops typically give different specifications for the two groups. For example, for telescopes I'll often see focal length, aperture ratio, or limit value, but I haven't seen any of those for binoculars; for binoculars, on the other hand, they'll mention exit pupil, field of view, or glass material, none of which I've seen given for a telescope. Why is that? Are the two devices so different as to be incomparable?


texts: Does Hawking Radiation really exist and Why "negative energy" in virtual particles?

texts:
I'm doing some research on black holes for a science video contest - more specifically, on Hawking Radiation. As far as I know, there are these constant quantum fluctuations of "virtual" particle pairs (basically particle-antiparticle) that appear, then almost instantaneously mutually annihilate. Near the event horizon of a BH, if one virtual particle gets trapped inside, then it acquires negative energy, while the other particle escapes away and is emitted as radiation. My question is, why does the virtual particle that's sucked in get negative energy? Is it due to some rotating vector stuff or is it inherent in the particle?
And, as per my logic, if NASA detected this image of a BH, it's clear that it's emanating some radiation, so Hawking Radiation has to exist, right?
Any help in clarifying or correcting my understanding would be appreciated.Thank you.


texts: On a log-log plot of surface gravity to planet mass, what is the meaning of the y-intercept?

texts:
I am playing around with data from exoplanets.org, and am interested in the plot of surface gravity to planet mass. I reproduced this plot  after downloading their data and performed a non-linear regression model to fit the curve. Unfortunately,the covariance matrix of my fit has infinite values, so I am now trying out a linear fit on a log-log plot, shown below.  My fit, for $y=ax+b$, is $a=0.9511$, $b=0.8631$.

I am now thinking about what I am plotting. I suspect there may not be anything interesting in $\log \frac{GM}{R^2}$ vs. $\log M$, but, regardless, I am trying to understand if there is any meaning in the y-intercept.

What are possible explanations for the value $b$?


texts: Why do Seyfert Galaxies emit less energy than Quasars and Blazars, and how is the emitted energy measured?

texts:
When I was reading information about QSOs on a website, it said that Seyfert Galaxies emit less energy than Quasars and QSOs.

Why do Seyfert Galaxies emit less energy than quasars, and how is this energy measured?


texts: Orbital path projections onto a 2D plane

texts:
In ProfRob's excellent answer to Is S2 still the fastest known star in the galaxy?, he posted a figure of the orbital paths of stars passing close to the supermassive black hole near the center of the galaxy, which I am re-posting here:

This figure caused some confusion in the comments, especially concerning the fact that there doesn't seem to be a common focus for all the ellipses in the image, as might be expected by Kepler's First Law.  ProfRob reminded the other users that the figure was a projection of the orbits in 3D onto the plane of the sky.
Question: How are the geometric properties of orbits conserved (or not) when projected onto a plane?
Specifically:

Are the 2D projections of ellipses also ellipses?
Do the ellipse projections all contain the corresponding projection of the central mass?
Why don't the ellipse projections share a focus?
Under what conditions (if any) will the projections share a focus?


texts: What is a "differential chemical abundance"?

texts:
Probably this is a extremely basic question, but after a lot of time searching about it without results (in all the sites/publications i've found they only use this term but there is no specific definition)i came here with the hope of get an answer to my question: in the context of chemical abundance in stars, what is a differential abundance?

I already know what is a chemical abundance, the question is simply about the implication of the "differential" word.

Specifically, my doubt emerged when i was reading this publication.
In the second paragraph of the section 3.2 "Stellar Parameters" is the first encounter with this concept:

  We adopted the same line list as in Ramírez et al. (2014). The
  EW  measurements  were  used  to  obtain  elemental  abundances
  with the
  abfind
  driver of MOOG (Sneden 1973), using Kurucz
  model atmospheres (Castelli & Kurucz 2004). Then, line-by-line
  differential abundances were obtained.

  The stellar parameters
  $(T_\text{eff}, \log g, {\rm[Fe/H]}, v_t)$
  of HIP 68468
  were determined by imposing a differential spectroscopic equilibrium  of  iron  lines  relative  to  the  Sun  (e.g.  Meléndez  et  al.
  2014a), using as initial parameters the values given in Ramírez
  et al. (2014). The solar values were kept fixed at
  $(T_\text{eff}, \log g, v_t)
= \rm
(5777\,K, 4.44\,dex, 1.0\,km\,s^{-1})$. Our solution for HIP 68468
  gives consistent differential abundances for neutral and ionised
  species of different elements, and also for atomic and molecular
  lines, as discussed in more detail in the next section.


texts: Is the whole universe is rotating on an axis?

texts: Most of the celestial bodies we know are rotating or spinning on its axis.Is there any chance for the universe to rotate on its axis?


texts: When will the Milky Way "arrive" at the Great Attractor, and what all happen then?

texts: The Great Attractor is described as a location to towards which the Milky Way, along with all other galaxies in the Laniakea Supercluster are moving. How long will it take for the Milky Way to "arrive" there, and what will happen when it does — what, in fact does "arrive" mean in this context?


texts: How precisely we know the Gaia spacecraft baseline? [Question related to Planet 9 and the cosmic distance ladder]

texts:
The European Space Agency mission Gaia is performing an outstanding job by measuring the parallaxes of almost 2 billion stars, many of which are thousands of light years away from the Sun. For this amazing archivement, two main things are needed: 1) An accuracy of less than a milliarcsecond when measuring angles with respect to distant quasars (which it uses as a reference frame) and 2) An accurate measurement of the parallax baseline (which is not exatly 2AU since Gaia is located in L2 and the distance to the Solar System barycenter is not always the same).
My question is about the second of these measurements. How precise is the distance between Gaia and the Solar System barycenter currently known?
In a recent paper it is said (if I read it correctly) that the position of the planets with respect to the Solar System's barycenter is known within uncertainties of the order of $\sim 100\;m$. I guess this was archived with lots of observations coming from radar ranging echoes bouncing over the planets and radio links from planetary probes (correct me if I'm wrong, I would like to know more on this).
In another paper I read that:

The location of the barycenter relative to the Sun, Moon, and planets
depends on the set of bodies modeled. In particular, inclusion of
trans-Neptunian objects such as Sedna and Eris in the ephemerides from
the Institute of Applied Astronomy causes a difference of the location
of the barycenter with respect to the Sun of about 100 km.

Which made me wonder if the addition of large unknown Solar System bodies, like the hypothetical Planet 9, would change significantly the parallax baseline of Gaia as to make the distances to stars wrong by much (this in turn would make the Cepheid distance estimator more unreliable and that in turn galactic distances up to the entire Cosmic distance ladder, possibly affecting the value of the Hubble constant in the end). Am I mixing things (models and actual data, direct and indirect measurements)? Our distance measurements inside the Solar System are accurate enough to avoid any of these issues really?


texts: What explains the distribution of new impact craters on Mars?

texts:
24 minutes into this van Karman lecture by Dr. Tamppari, the slide below is shown with symbols for transient events on Mars. Red dots represent meteoroid impacts which have occurred while MRO has been in Mars' orbit.

New impacts are almost only found at lower latitudes. And longitudinally there are two equally sized gaps at the equator. Is this because of some observational bias or is there a natural explanation?


texts: What will happen to the shape of a galaxy when a super massive black hole lying in its center dies(evaporates out)?

texts:
What's at the Center of the Milky Way?
 In this article it is said that a supermassive black hole lies in the center of milky way galaxy.

  At its center, surrounded by 200-400 billion stars and undetectable to the human eye and by direct measurements, lies a supermassive black hole called Sagittarius A*, or Sgr A* for short.
  The Milky Way has the shape of a spiral and rotates around its center, with long curling arms surrounding a slightly bulging disk. It's on one of these arms close to the center that the sun and Earth are located. Scientists estimate that the galactic center and Sgr A* are around 25,000 to 28,000 light-years away from us. The entire galaxy is around 100,000 light-years across.

We revolve around the center every 250 million years.Presumbably we rotate beacuse of the BH.

When the black hole dies in our galaxy will we be thrown out of the revolving orbit?

The shape of the galaxy is expected to change right?It will be some irregular shape not spherical?


texts: How can I calculate the orbital periods in a binary star system?

texts: I have two stars, with known masses and known orbital radius. How do I calculate the orbital periods of both stars?


texts: How difficult is it for an amateur to discover a new exoplanet or astronomical object?

texts: I recently read about precovery, where plates or images of an object predating its discovery are used to precisely determine its orbit. It occurred to me that it might be possible that some objects have yet to be identified in open-access astronomical databases, simply as an oversight or maybe as a misidentification (say, mistaking a planet for a star). Is it possible for an amateur astronomer to go through open-access astronomical image data and perhaps use machine learning algorithms to find new celestial bodies? Has it been done? If not, how likely is it that an amateur astronomer could even do so?


texts: Determine distance of asteroid based on two observations from different locations

texts:
Two astronomers A, B located in different regions A: 17° E, 46 ° 27 'N,
B: 17° E, 22 ° 34 'S observe an asteroid at the moment it is exactly above the meridian and is in position C which is a distance a from A and b from B.
Both observe from sea level and astronomer A sees the asteroid 25 ° south of his zenith, while astronomer B sees the asteroid 45 ° north of his zenith.
Consider the radius of Earth equal to 6400km.
Calculate the distance of this asteroid from the center of the Earth.
My work: We can create two triangles for example triangle AEC and BEC(Where E is the center of Earth) and from the data we have one angle for each (EAC = 180-25=155 and EBC=180-45=135) and one known shared side which is the radius of Earth. This is how far I have gone I suspect using law of sines and cosines to find some relations and do a system of equations but whenever I try and solve the system the numbers don't make sense.
Any ideas on how to continue with the soution will be appreciated.
Thanks in advance for your help.


texts:
Is Cosmological inflation still considered as hypothesis?
Is CMBR evidence not enough?


texts: Mars is differentiated, with a core, a mantle and a crust. There are no (longer any) plate tectonics on Mars. Does this mean there is no convection in the mantle? Could there be convection in the mantle without it causing plate tectonics?


texts:
It is well known that diffraction resolution of a telescope depends on the exterior radius of aperture: One can, for instance, use just a narrow outer ring of a parabolic mirror and the resolution will be the same as it were the whole mirror (obviously, intensity will be much much smaller).

Now, take such a ring telescope, say, 3cm wide ring which is 100 meters in diameter.

Suppose we are using adaptive optics. How many actuators are needed to reach the maximal possible resolution?

I assume that spacing between the actuators should be of an order of Fried radius r0 (i.e. one actuator about every 10cm along the circumference of the ring). I.e. number or actuators should be of order D/r0, where D is the aperture diameter.

Is it correct?


texts:
I'm sure Caltech has answered this in some way, but I think it's a good question have on this site.
What good evidence exists for the 9th planet as spoken of by Caltech?
As I see it, Caltech has apparently looked at the orbital parameters of many Trans-Neptunian-Objects (TNOs) and noticed that the lines between their perihilion and aphelion (I don't know what the technical term might be) all run more or less in the same direction. This is evidence that some large body has gravitationally "synced" these planets over millions of years.
Except that alone isn't good evidence. Here are two stats first:

Known TNOs: about 1,750 according to the Minor Planet Center's list.

Estimated existing Kuiper-Belt Objects: 120,000+ according to Britannica. (That number is only estimating objects of 100-km diameter or more, but that's fine for our purposes.) Note: 120,000 is only for KBOs. There are other TNO sets such as the oort cloud (and the scattered disc if you define it separately), so I expect the number to be much much bigger than 120,000.

Given that we've only measured about 1% or less of TNO orbits, how can we be sure we have a good random sample to say that a massive body must have aligned these orbits? In other words, all the other orbits might be randomly distributed, which would be compelling evidence that some giant body is not "syncing" orbits or else way more than 1% of them would be "synced".
If I recall my statistics class correctly, 1% is not good enough for a random sample. The border-line good enough area starts at 3%, but there's still a catch: It has to be a random sample. There are still observation-bias questions here because obviously we've only mostly discovered the "nearby" TNOs, because they are easier to discover when they're "nearby". That certainly would not be a random sample even if we had 3% of them.
TLDR: There are at least 100,000 distant objects, of which less than 1% of them have some kind of aligned orbit as far as we know today. Is this actually good evidence that something has aligned them?
EDIT: Another analogy that might help. You have a bag of 100 marbles. You reach in and pull out 5 from the top of the bag (notice I didn't say any random 5!). They turn out to be 4 red ones and 1 black one. Is this actually good evidence that about 80% of the whole bag is red?


texts: The sun is a big ball of hot plasma which contains free electrons. However, how does the absence of metallic elements in the sun generate the magnetic field to orchestrate these free electrons to display such beautiful solar phenomenon?


texts: If you put all planets between earth and moon what would happen?

texts:
It's often discussed that you can fit all the planets in the space between the Earth and the Moon. But if they actually did teleport there instantly what would happen next?

Assuming their initial direction and velocity was the least problematic, the most likely to "work". Would they all smash together or fling apart? Or do we have any idea?

https://futurism.com/you-can-fit-all-of-the-planets-between-earth-and-the-moon


texts:
wiki says that average distance from earth increases 3.8 cm per year, can you tell how much of that is due to the expansion of the universe?

wiki also says:

  Through the action of tidal forces, angular momentum is slowly being
  transferred from Earth's rotation to the Moon's orbit. The result is
  that Earth's rate of spin is imperceptibly decreasing (at a rate of
  2.3 milliseconds/century),[20] and the lunar orbit is gradually expanding.

Can you give some details about this process, is the orbit changing shape, eccentricity? is the average orbital speed decreasing, by what value? is the spin angular velocity increasing, by what value?

If I did not misunderstand it, the current view on tides says that tidal bulges exert a torque on the moon, and L is tranferred to it, if that is correct, that L being transferred to its spin is increasing or decreasing it? Can you clarify also how a torque on the spin can produce a change of the orbit, which only implies a change (a decrease, in fact) of its orbital speed and not of the spinning speed? Can the spin (L) influence the orbital L, and how?

edit

I asked specific questions, which are not asked or answered there. In particular I am asking: if as they say the tidal/equatorial bulge increases spin angular momentum, how is this transferresin its turn to the orbital angulat momentum? Or, alternatively
can gravity directly increase the orbital momentum of a satellite?
Actually the answer, besides being incomplete, may be wrong because momentum/KE is not added , but subtracted to the moon, since its orbit gets larger. There can be no transfer, since both earth and moon are slowing down
torque is not correctly explained


texts:
I am interested in buying a telescope and I would like to use it to look at like galaxies and nebulas.

Right now I'm looking at a 130 mm fast (f/5) Newtonian that comes with two eyepieces of 10 and 20 mm focal length. It comes with a tripod and German equatorial mount that includes fine motion controls for both axes.

This seems about right for what I'd like to do. It's going to be my first telescope and first time to try to look at galaxies and nebulas.

What are other considerations I should weigh before choosing the final one to purchase? Which features might be most helpful for a beginning observer looking for faint objects?


texts:
Consider the vector positions of the center of mass of Moon, Sun and Earth, $\vec{r}_{\rm M}$, $\vec{r}_{\rm S}$, $\vec{r}_{\rm E}$, respectively, in a given reference frame.

Consider:

the angle between the vector $\vec{r}_{\rm S} - \vec{r}_{\rm E}$ and $\vec{r}_{\rm M} - \vec{r}_{\rm E}$,
the angle between the vector $\vec{r}_{\rm E} - \vec{r}_{\rm S}$ and $\vec{r}_{\rm M} - \vec{r}_{\rm S}$,
the angle between the vector $\vec{r}_{\rm E} - \vec{r}_{\rm M}$ and $\vec{r}_{\rm S} - \vec{r}_{\rm M}$.

Does any of these angles have a name in astronomy, or can be important for some specific reasons? If so, may you please give me some general indications of why this is the case, and point to some references?


texts: Chances of life on other planets, how watertight is the idea that 'As soon as life could occur, it did occur’?

texts:
I’ve heard it reasoned that ‘Almost as soon as life could occur on Earth, it did. Therefore it seems likely that life develops easily, and thus that there’s probably lots of life out there’.
Is this notion undermined by any of these things?:
– If life develops easily, it’s likely to have developed independently multiple times on Earth (any evidence of this?).
– The fact that life developed soon after particular conditions emerged indicates only that that’s what happened on that occasion. It doesn’t indicate frequency. It might occur once every trillion years under those circumstances.
– Life could happen under many circumstances that life as we know it doesn’t exist. If there’s no evidence it did on Earth under different conditions, how does the reasoning hold?


texts: Was Milky Way formed after Sagittarius A Explosion?

texts:
Is it possible that most galaxies (and our galaxy) were formed from leftovers of supernova explosions?

In order to have a black hole 4,000,000 x solar mass the initial mass of the star should have been even greater.

So I was thinking, is it possible that after the big bang, gas formed much bigger stars 1,000,000,000,000,000,000,000x bigger than the sun, which later exploded forming:

black holes in the middle of future galaxies
Gas, which later created smaller stars, planets, etc.

Am I trying to reinvent a bicycle here?


texts: Why can we sometimes see the moon during the day?

texts:
At some points in the year, the moon at my location can be clearly visible during the day. Why is this?

If it is any help, I live in Alberta, Canada.


texts: What's the name of the point where you are closest or furthest from the ecliptic?

texts:
Every 24 hour day, there is a point as the earth rotates about its axis, where a location on earth is the closest to the ecliptic and where it's the furthest. Do those two points have a name?

What I mean is on the plane of the ecliptic, as the earth rotates around its axis, a point on the earth at 45 deg north is going to hit a low-point perpendicular to that plane, and will hit a high point perpendicular to that plane.


texts: Has the Penrose process ever been linked to an observed phenomenon in some way?

texts:
This answer to What defines the plane of an accretion disk around a black hole? mentions the Penrose process as a potential mechanism that could change the axis of the orbital angular momentum of an accretion disk around a black hole away from the original axis of the infaling matter's source (e.g. a companion star, a galaxy) and towards the the black hole's axis of rotation.
Here I'm just asking if the theoretical Penrose process has ever been linked to an observation, or has been used as part of a potential explanation of an observed phenomenon.


texts: Why there is no axis measurement when telling distance between objects in space ?

texts:
What's in upper part in our galaxy ?
If space is 3 dimensional, what lies beneath solar system, or in upper part ? Why it seems from every graphical view of solar system / galaxy, everything is in one single axis ?


texts: The defintion of star/planetary/solar system

texts:
In many science fiction stories, we hear the term star system that mostly refers to a star and its planets. This is often used interchangeably with the term solar system. But after some research I understand this:

Planetary system refers specifically to anything orbiting a star that is not a star itself. According to Wikipedia, this generally refers to the planets, but may include other objects like asteroids and dwarf planets. It does not refer to the star itself.

Star system refers to any system with two (binary) or more (multiple) stars, but only the stars themselves, not planets or anything else.

Solar system generally refers to our own Solar system but there are situations where "solar system" (lowercase) refers to a star and the planets or other objects orbiting it (as long as something orbits the star).

So, is it incorrect to use the term solar system/star system to refer to a star and its planets?


texts: Does this CHEOPS first light image imply bad astronomy?

texts:
@KeithMcClary's comment under lousy mirror corrected by software links to Bad Astronomy's First Light for the Exoplanet Hunter Mission CHEOPS Goes Tetrahedral which shows the image below.
I understand that in order to do precision photometry with a pixelated sensor one wants to spread the light over several pixels in a controlled way, but is this particular PSF the result of some painstaking optimization, some problem with the figure of one of the telescope's elements (oh no I hope it's not 1990 all over again!) or just because it's preliminary and they'll tweak something to make it more symmetrical?
If it stays this way, will it degrade CHEOPS' performance?

CHEOPS launched on 18 December, 2019, and on 07 February, 2020, it took its very first image of a star! The target chosen was HD 70843, a star about 155 light years away that’s a little bit hotter and brighter than the Sun.
The image, traditionally called First Light by astronomers, is itself … surprising.


texts: If there are indeed multiple universes, where do they exist? We "know" that outside our universe, consisted of spacetime, there is nothing - i.e. 0 dimensions, no space and no time. So "where" are other universes, how would the distance between our space and other be measured inside nothing?


texts:
Is there Rotational inertia of the Solar system as one entity "disk"?
Is this even possible?
Edit:

The angular momentum of a multi-point system in the Solar system - Since the different planets have different mass and orbital periods then how does create angular momentum, inertia in the system?
How can one planet affect another planet in the system from its individual rotation?
Does the solar system exhibit rigid body rotation from the mass distributed over planets?


texts: Is the influence of gravity instantaneous?

texts:
When I was in college, I posed to my astronomy professor a thought experiment that had been puzzling my mind for some time: "If all the matter in the Sun magically disappeared instantly, how long would it take its gravity to stop having an effect on us?" His response was that the force of gravity is instant, unlike the speed of light, which appears instant.

My big question is: "Do we know it's instant?" We can't possibly move an object large enough to have a noticeable gravitational influence fast enough to measure if it creates (or doesn't create) a doppler-like phenomenon.

If he was wrong, how do we know it's not?


texts: How to mathematically describe a planet's eccentric orbit?

texts:
Is there a formula for describing a planet's position along an eccentric orbit over time? I am particularly interested in the elliptical case (0 < e < 1).

I understand that the planet has a higher velocity closer to the perihelion. Ideally I would like to be able to calculate a planet's position on it's orbital path in relation to how far through it's orbital period it is, if that makes sense.

Alternatively, is there software (that doesn't require a university's budget) to work this out?


texts: Dataset containing list of known globular clusters

texts:
Does anybody know if there is an existing dataset that consists of all known star clusters, their name, and their apparent dimensions or similar? Is it possible to make a query to, or download all SIMBAD objects that are of type "globular cluster"?

Thanks


texts: Can young surface of Venus be caused by early oceans instead of global resurface event?

texts:
There is evidence of a global resurface event on Venus: the craters are young and evenly distributed.

Is it possible that there is another reason: Venus had a very deep ocean in the past, and that hindered formation of craters on the young planet

Venus is believed to have had a large amount of water when it formed, but the water molecule has been broken down due to lacking magnetic field for protection, and the hydrogen released has escaped from the planet.

My hypothesis is:

In ancient times, Venus had a very deep ocean
The very deep ocean prevents formation of impact craters on the ancient planet, so no old impact craters are found on the surface of Venus
Later, the water in the ocean was broken down into hydrogen and oxygen  by solar activity, so the water level decreased.
When most water had escaped from planet, asteroids can strike the crust directly and form impact craters.
As most impact craters can only be formed after the water escaped, so we can only find young craters at the surface of Venus.

Is my hypothesis possible?


texts: Visibility of earth from moon during day-time of moon

texts:
Inspired by this question. I am curious whether earth, besides being nearly fixed on one place on the moon's sky, is it visible during the day-time on moon too?

My understanding is that earth should be visible as moon has no atmosphere. Also, if the NASA didn't edit the following photograph, it suggests that the day-time sky of moon is all black and earth should be visible in it.

I think, Stellarium don't take into account the atmosphere once you are on other planet.


texts: At what size do objects burn up in the atmosphere when falling from orbit?

texts:
As the title suggests, I am wondering the maximum size an object can be so that it will completely burn up when entering and falling through Earth's atmosphere. I'm focusing on man made objects, not asteroids or meteors. Also, how much does the make-up of the object affect its burn rate? I.e. metal vs plastic vs glass, and so on.
Thanks!


texts:
I always assumed that Wolf 359's discoverer had been Max Wolf, but I just found out that he simply measured its high proper movement and included it in his star catalog.

Since Wolf 359 is a very faint star that can only be observed with a large telescope it is clear that it was unknown in ancient times and that some astronomer must have been the first to observe its existence.

Are there any data on who was the first observer of Wolf 359? If not, in which star catalogue or other map was it first included?


texts: Meteor shower predicted to be best viewed BEFORE midnight (for reasons other than the moon)?

texts:
Reading that the Leonids meteor shower is almost upon us, I clicked some links (e.g. EarthSky.org and NatGeo) to read more of the prediction; especially the part about when to best view them.

I had a Déjà vu when I saw "early morning hours" because it seemed to me that "that's what they always say".

I'm guessing that it's not a coincidence that the constellation for which the shower is named always seems to rise around or after midnight at the time of year when the shower occurs.

So I'd like to ask if this is true, that they pretty much always are best viewed after midnight (except when issues of weather or the Moon interfere), and if there has ever been a shower where this wasn't the case — one that was best viewed before midnight.


texts:
The planets rotate as an after effect of their creation, the dust clouds that compressed span as they did so and the inertia has kept it rotating ever since.

It's fairly easy to prove that planetary bodies are rotating just by watching their features move across their respective horizons.

This seems less easy to discern for amateur astronomers  in the case of the sun though.

Does the Sun also rotate as a by-product of it's creation? What evidence is there to support this? Does the sun have any discerning features that make it evident it is rotating?


texts: Is Betelgeuse is continually expelling material on the scale of the 2019/2020 event?

texts:
The AUGUST 13, 2020 Phys.org article
Results from Hubble suggest that Betelgeuse's recent dimming was due to material ejected from the star says:

...the star's unexpected and significant dimming periods in late 2019
and early 2020 were most likely caused by the ejection and cooling of
dense hot gases

and links to Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse in Ap.J.
I assume that the blue shift caused by the convection cells moving outward was detected because it was directly in our line of sight to the star, if a similar event occured at right angles to us, Hubble wouldn't detect it so easily.
My question is how likely is it that Betelgeuse is continually experiencing events like this that are not visible to us because the opaque material is not between the Earth and the star?


texts: Simulate earth, moon, sun constellation with dates

texts:
I would like to simulate the three object distance, specifically the distance of the moon to both, sun and earth for further investigation into tide prediction.

What would be a good starting point to browse?
Do any (preferably python) libraries exist for this?
My use is to query the function with a date and it would spit out the distance.

A first model I would be happy to start with would be basic circular trajectories and expand to elliptical & inclinations from there.


texts: Build a high quality telescope from scratch

texts: I am interested in building a high quality portable telescope from scratch in an attempt to better understand how telescopes work. What kind of materials do I need? How would I go about putting the telescope together? Are there any online guides that you can recommend?


texts: Does this black hole mass/galaxy stellar mass relation hold for extremely low-mass galaxies?

texts:
I read a preprint last week (Palmese & Conselice 2020) that suggested that the recent gravitational wave detection GW190521 could be the end result of a merger of two extremely low-mass galaxies. Each black hole would have originally been at the center of one of the two galaxies, and the two would have coalesced $\sim4$ Gyr after the galactic merger.
The scenario requires two ultra-dwarf galaxies of masses $M\sim10^5\text{-}10^6M_{\odot}$. The authors calculate this by using a power-law relation between the galactic stellar mass $M_*$ and black hole mass $M_{\text{BH}}$ empirically found by Reines & Volonteri 2015:
$$\log(M_{\text{BH}})=\alpha+\beta\log(M_*/10^{11}M_{\odot})$$
However - as with some other assumptions Palmese & Conselice make - this power-law was derived by looking at much more massive galaxies, with the great majority falling in the range $10^{9.5}M_{\odot}<M_*<10^{11.5}M_{\odot}$. Even the lowest mass galaxy in that sample lies just under $\sim10^{9.5}M_{\odot}$.
My question, then, is this: Can we extrapolate this sort of purely empirical result to the extremely low-mass galaxies that would have been involved in the merger? My guess is not necessarily, and the authors only used this form because of the sheer lack of data involving low-mass galaxies with extremely low-mass central black holes - it seems difficult, if not impossible, to detect black holes of $60\text{-}90M_{\odot}$ in low-mass and presumably very dim galaxies outside the local universe.


texts:
A little bit of context:
I dabble in amateur astronomy, however only very lightly. I originally wanted to make some observations of Mars because I know it is supposed to be very close these days but unfortunately in the Netherlands where I live we are having very bad weather. However, I think I spotted it today in the evening coming home (sadly I did not managed to get home quickly enough for a telescope/binoculars) and it was quickly gone behind clouds. However, I am not sure if it actually was Mars. It seemed too bright. My place is close to very active airport (Schiphol) and sometimes with just naked eye planes can look like celestial bodies (when they move away from me it looks like they don't move at all and I only had chance to look at the object for 2-3 min).
Information about Location & Object:
I took photo of the object with my phone (see below).
It was very bright - I recently (during summer) did some observations of Venus & Jupiter and this object outshined them both (although they were not visible today due to clouds so I am comparing it to my imperfect memory).
I immediately looked up my location on my phone: 52.294 N 4.879 E elevation 0 meters and the local time was 21:42 GMT+2.
The object was in the direction 110° East.
Now, I already looked it up and Mars should be in that direction, but I worry it might just have been a plane.
Furthermore, it looks like it is little bit too high. When I did observations of other planets in the past they were much lower in the sky. I know that the position changes due to Earth's rotation and orbit around the Sun, but I can't remember seeing them so high up and as far as I understand planets are all roughly around the ecliptic (although this was not place where I usually go stargazing so I might just be getting confused). Hence I would like to know, is the object in the picture Mars or we can't tell or it is something else?


texts: Compared with similar stars, does the sun itself have properties that make life on Earth possible?

texts:
We often hear our solar system has properties for life. For example, it is far away from the center of Galaxy. It has Jupiter far away to protect us from asteroids. It has optimum size of territorial planets, plate activity on Earth, and so on.

But besides that, compared with similar stars, does our sun itself also have properties that make life possible? For example, does it have extra stable brightness? Or does it emit less high energy radiation?


texts: Expected nature of LISA's data; will it be more like a forest of static peaks, or a series of individual events?

texts:
@RobJeffries' clear answer to Which things “LIGO can see things that LISA can't”, and vice-versa? explains that the Laser Interferometer Space Antenna or LISA will only be sensitive to gravitational waves with frequencies below about 1 Hz and so will be sensitive to much slower rotating objects than those that LIGO records.

  Lower frequency GWs can only be seen with LISA. This would include stellar binary systems with orbital periods longer than about 10 seconds, merging supermassive black holes and maybe GWs from the big bang

This can might include "event-like" signals, for example (possibly) a merger of two supermassive black holes that are so large in diameter that even during the merger their orbital frequency is below 1 Hz, but it can also include signals from the rotation of bodies not yet in contact but are slowly losing angular momentum though continuous GW radiation. While these would be much weaker, they would provide a very stable and very narrow peak in a spectrogram with an extremely slow drift, so you could accumulate data for years in order to bring them up out of the noise.

While LIGO's detected events have lasted of the order of 1 second or less, it sounds like it is possible that LISA could potentially record continuous GW radiation from a large number of pairs at the same time since the "lifetimes" might be years or millennia rather than seconds, provided that the sensitivity to these weaker signals is sufficient.

Question: What is the expected nature of LISA's data; will it be more like a forest of fairly static or slowly moving peaks in frequency space, or a series of individual events? Presumably this has been modeled based on some predictions of the number of different kinds of pairs at various separations expected to be found nearby.


texts: Does Saturn raise tides on Titan's lakes?

texts: Titan is the only body in the Solar System other than Earth to have large bodies of surface liquid. Since Saturn is much more massive than the Moon, I would expect for tides, if they're present to begin with, to be much larger than the ones here on Earth.


texts: Lunar phases if Earth was tidally locked to the Moon

texts:
I know that the Earth will never become tidally locked to the Moon, so this is purely hypothetical.

If I understand correctly, in this hypothetical scenario an Earth day is now a lot longer at around 29 current days, and you can only ever see the Moon from half of the Earth.

So standing on the "lucky" side of the Earth you should be able to see all the lunar phases during a single night. The Moon become gradually more illuminated, peak as a full Moon and then darken as the night ends.

Is this correct?


texts: What observation can be expected on LIGO if any when Betelgeuse goes supernova?

texts:
What observation can be expected from the LIGO†  gravitational wave observatory if any when Betelgeuse goes supernova?

Could we know that Betelgeuse has gone supernova before we see it light up our night sky?

†or other current or soon-to-be completed gravitational wave obervatories


texts: Why does Earth have a dip in the CO2 absortion spectrum from 14 to 16 micron?

texts:
This paper shows that there is a dip in the CO2 absorption spectrum of Earth. In essence the trough of the absorption of CO2 for Earth is cut into two separate troughs instead of 1 large trough. Why is that?

original without arrow
As there have been some comments on whether this is planet related or molecule related, here is an additional image which shows the absence of the double trough in the CO2 absorption pattern for Venus whilst showing it for Earth:


texts: What is the furthest object in the observable universe?

texts: My question is about furthest object in the observable universe except Сosmic microwave background.


texts:
This website (page 26) claims that full-earth-shine on the moon is 100 times greater than full-moon-shine on earth. The figure 100 is made up of the difference between the size of the earth and the moon, multiplied with the difference of their albedos. The earth is 13.45 times bigger than the moon. 100 divided by 13.45 equals 7.43. 7.43  multiplied with 0.12 (the moons albedo) equals 0.8916. Thus, he must have calculated with an earth albedo of 0.8916. But that might be a miscalculation. To figure that out the following question needs to be asked:
What is the highest albedo of the earth's surface facing the sun ever measured? Note, the question is not about the albedo of certain sections of the earth, but about the whole side of the earth that is facing the sun.


texts: Measuring the size and the geometry of Universe

texts: When we would be able to tell with surety that universe is finite or infinite? How can we exactly determine the density of the universe so, that we compare it with critical density, in order to determine its geometry? Does the infinite Universe entails infinite black holes or infinite stars?


texts: What would be the practical consequences (on earth) if the Moon was not tidally locked?

texts: I was thinking about the fact that all the largest Solar System moons are tidally locked to its primary and this question arose.


texts: What is the effect of this expanding universe on the energy density of it?

texts:
We know that our universe is expanding i.e.  volume of the universe is getting larger with time with total energy being conserved. My question is whether the energy density is getting smaller with time.
If this is true then what is the effect of this phenomenon on all the celestial bodies?


texts: Does the current "fainting" of Betelgeuse show any spectral trends that differ from it's normal variability?

texts:
update: With all the newest news about  including what the Dr. Becky video discusses as linked in How do magnetic fields mess with astronomers' observations? I'll bet this question can now be answered!

The Astronomers Telegrams #13341 The Fainting of the Nearby Red Supergiant Betelgeuse and #13365 Updates on the “Fainting” of Betelgeuse (both in December 2019) discuss the importance of measuring color temperature and spectral features of the needed observations.
So far, does the current Did the recent fainting episode show the same kinds of spectral changes behavior as the irregular but more limited variation in brightness, or does did it contain a dimming component that affects it differently, for example as intervening material (e.g. dust, debris, broken planets) might do?
Betelgeuse, Betelgeuse, Betelgeuse, there, I said it, now let's wait 700 years to see what happens.


texts: Why do Uranus' and Pluto's moons orbit the equator? What makes a moons' inclination tilt with the rotational axis of their planet?

texts:
Uranus and Pluto have their axes of rotation almost 90 degrees towards the ecliptic. But why do their moons tilt the same way?

Does it mean that their tilts were caused by passing near some external mass that affected the planet and its moons equally, rather than some planet specific process such as a comet impact or tectonics?

Mars' rotational axis tilts over time, but its moons today are spot on over its temporary equator. Earth's moon is aligned with the ecliptic and doesn't seem to care about our planetary tilt, although (or because of?) oceanic masses tugging on its tides. Exoplanets have been found that don't orbit in alignment with their star's rotation, and why would they do so billions of years after formation?


texts: Converting rectangular to polar coordinates

texts:
I'm following the steps in this paper on how to calculate geocentric longitude. In section 3.4.2 it says the
Geocentric rectangular co-ordinates of Mercury then are:
Xg = Xh−X0 = 0.990 A.U.
Yg = Yh−Y0 = −0.259 A.U.

Converting these into polar form, we get the geocentric distance and longitude as:
rg = √(X2g+Y2g) = 1.024 A.U.
λg = tan−1(Yg/Xg) = 345.3◦.

For the life of me I cannot get the inverse tan of (Yg/Xg) to give me 345.3. This is what I'm doing in python:
Xg= 0.990
Yg= -0.259
math.degrees(math.atan(Yg/Xg)) = -14.66091789971255

Any help greatly appreciated.


texts:
I saw this picture on the BBC news website.

There appears to be a ring of craters in the center of the picture, aligned in an approximate sub vertical orientation.

Am I just seeing things or does this apparent ring of craters a feature and does it extend to the far side of the moon? If it does exist, what form of bombardment or gravitational attraction would have create such a ring?


texts: How was the acceleration calculated for this CME (Coronal Mass Ejection)?

texts: I am looking at data used in a project to get the velocity and acceleration of a CME (Coronal Mass Ejection). I understand how the velocity was calculated, and for the acceleration, I get the v2-v1 part of the formula for acceleration that was used (ex. 306.5-331.2), but what time intervals (t2-t1) were used to calculate the accelerations?


texts: How to calculate the time for the solar disk to pass the horizon and transit's lines

texts:
For a given date, longitude, and latitude:

Popular apps and websites give the time when the sun's center or edge is on the horizon (i.e., the time of sunrise and sunset) or its transit (i.e., noontime), but I want to ask how to calculate the time needed for the solar disk to pass the horizon's line and the transit's line (preferably in c# or java)?


texts: What is the significance of the velocity resolution in spectral line observations using radio interferometry?

texts:
I've always struggled to conceptualize the term "velocity resolution" in spectral observations. In principle, it is simple to calculate. For example, one can take the spectral width and divide it by the number of channels. ie. A 16 MHz wide window with 4096 channels yields a 3.906 kHz / channel velocity resolution. For an observation centered on the H1 spectral line, we get 0.82 km / s / channel utilizing the speed of light and the photon energy at the 21-cm H1 line ~ 1.42 Hz.
So, why is there a "velocity" defined in the resolution term? I understand dimensionally it comes from the speed of light, but what does the final velocity signify? Does it have anything to do with how the source moves (ie. object of interest is moving) with respect to the observer? Is it better to have a larger or smaller velocity resolution or does it depend? In general, why is the value important? Thanks in advance!


texts: Is there a relation with the noun planet and to be in a plane?

texts:
This morning I was in the shower and it struck me that the word planet might be related to the fact that the PLANEts orbit the sun in a PLANE. Did this naming somewhat happen by accident or was it consciously chosen? If it is the former then I'm simply mindblown by the fact that I didn't see this relation before.

I quickly looked up the etymology on the word planet, which comes from Greek and means wanderer/wandering. Nonetheless, could there still be a relation, both words might stem from the same origin...?
Thanks in advance!


texts: Why is the magnetic axis of Uranus and Neptune off center?

texts:
It(Uranus) rotates on its side, tilted almost 98 degrees from the plane of its
orbit around the sun. The axis of its magnetic field is tilted too, at
a 59-degree angle from the rotational axis. The magnetic field is also
off-center, with the field lines emerging about a third of the way
toward the south pole. (source)

Neptune's magnetic field is tilted 47 from the planet's rotation axis
and is offset at least 0.55 radii, about 8,500 mi (13,500 km) from the
physical center. The dynamo electric currents produced within the
planet, therefore, must be relatively closer to the surface than for
Earth, Jupiter, or Saturn. Because of its unusual orientation, and the
tilt of the planet's rotation axis, Neptune's magnetic field goes
through dramatic changes as the planet rotates in the solar wind. (source)

So, it is well established that the magnetic axis of Uranus and Neptune is off-center and due to this, the planets faces the following consequences:

the magnetosphere  is irregular
the strength of magnetic field varies, almost opening and closing periodically as the magnetic field lines disconnect and reconnect
the orientation of magnetic field changes constantly.

But, why is the magnetic axis off-center in the first place? I found no source answering that. Is it due to alignment/orbit/internal heating mechanism of the planets?


texts: Does this video catch an Eta Aquarid - Earth skimming meteor?

texts:
I did a time-lapse animation looking towards the sunrise from Sydney, Australia on 25th of April.  You can see it here around 1m 25s in (that link should jump to just before it appears very near where the Sun is about to rise):

http://www.youtube.com/watch?v=lqr_KuLd2-c&t=1m25s

It then proceeds towards the right of screen over around the next 21 seconds (around 10½ minutes) before disappearing off the right. You might need to send the video to full screen to see the small white 'bullet of haze' that is moving against a very wide background.

One of my first thoughts was that it might be a meteor skimming the upper atmosphere, but I was less confident of that given it seemed to be coming from the general direction of the Sun, and I'd thought that was a direction unlikely to produce meteors.

That was until I read Eta Aquarid Meteor Shower in 2016 which states:

  The best time to view the Eta Aquarids is in the early mornings, right before dawn.

Well, at least that pins down the same time of day, if not the direction from which it came.

What is the likelyhood that this feature is a piece of comet debris that skimmed Earth's atmosphere?


texts: Could an ejected "extra ice-giant" still be lurking in distant solar orbit?

texts:
BACKGROUND

Hot Jupiters are thought to have migrated inwards, implying that another giant planet has been ejected in order to conserve the orbital momentum of those planetary systems. The number of interstellar "vagabond planets" has been estimated to be as many as the number of stars. And simulations show that if the Solar System started out with an extra gas giant next to Jupiter which was ejected, then one can end up with a very good fit with today's Solar System.

QUESTIONS

Where would such a hypothetical ejected ice giant be today? Should it be closer or further away than hot Jupiter-ejected planets because it is much smaller? Could it stay in an Oort cloud type orbit during several billion years (maybe ~15 orbits around the Milky Way) without being pulled off by passing stars? At what distance could we today observe a Uranus sized planet? Should it stay in the ecliptical plane or could its orbit have become greatly inclined when it was ejected?


texts: Calculating the Diameter of Jupiter through Image

texts:
I was trying to calculate the diameter of Jupiter from a picture I took of it. Here's the information I was able to get that I needed to calculate the diameter:

  Focal Length of Telescope: 1.2 m

  Multiplier for Barlow Lens: 2x

  Camera CCD (Sensor) dimensions: 14.8 x 22.2 (mm)

I found the diameter to be 135 pixels in my image. Here's what I did:

\begin{align}
f_e &= \text{Focal Length $\cdot$ Barlow Multiplier}\\
 &= 1.2 \cdot 2\\
 &= 2.4
\end{align}

Then, to calculate the field of view:

$$\text{Field of View} = \frac{\text{Sensor Size}}{f_e} \cdot \frac{180}{\pi}$$

Where the sensor size is the length in millimetres of the size of the camera CCD (I used the horizontal axis, or the longer side, to get the 135 pixels, meaning that I'd use 22.2 mm), and the second fraction is there solely to convert radians into degrees. Substituting my values, I got:

\begin{align}
\text{Field of View} &= \frac{0.0222}{2.4} \cdot \frac{180}{\pi}\\
&= 0.53^\circ
\end{align}

As my entire image is 4271.8 pixels wide, and I know the angular field of view, I used ratios to get the field of view of the 135-pixelled Jupiter to be $\theta = 0.017^\circ$.

Then, using basic trigonometry, I was able to calculate the radius of jupiter:

$$\tan \left(\frac{\theta}{2}\right) = \frac{\text{Radius of Jupiter}}{\text{Distance to Jupiter}}$$

The photo was taken on March 22, 2016 - Wolfram Alpha gives 667.6 million as the distance to Jupiter on that day:

$$\tan \left(\frac{0.017^\circ}{2}\right) = \frac{\text{Radius of Jupiter}}{667.6 \cdot 10^6}$$

$$\therefore \text{Radius of Jupiter} = 97\ 577\ \mathrm{km}$$

Googling the radius of Jupiter gives $69\ 911\ \mathrm{km}$ as the result. Is there any reason why my value is so significantly off? Anything wrong with my procedure, anything I'm missing? I was not able to to upload this image I took as the file size was too large, however, the image does not lack clarity and I am completely stumped as to why my result is off by such a significant amount.

Any help will be greatly appreciated, thanks in advance.


texts: What is a possible software for simulating binary star systems?

texts:
I would like to define both initial velocities and masses of components so that orbits may be either elliptical of hyperbolic. Is there any software to make such simulation?

Unfortunately, Binary Star Combined Solution Package is out of date and NASA online plotter supports only circular orbits.

Thanks.


texts: Why are asteroids with circular orbits rare?

texts:
Regarding this excellent question by Swike: Why are asteroids with zero orbital inclination rare?, I recently proposed that orbits with zero inclination are rare as a natural result of the statistical distribution of orbital revolution axes extended onto the celestial sphere.
In the below graph we see a similar sparsity of orbital eccentricities near zero. If asteroid orbital eccentricities were normally distributed about zero, wouldn't we expect them to be densest here?  What is the explanation?


texts: What is the apparent magnitude of the weakest stars we can see in one telescope on the ground with a diameter of 2.4m?

texts:
All I know is its main mirror diameter; 2.40 m

I also know that the eye, which its pupil is 5mm in diameter can see up to an apparent magnitude of 6.

How can I calculate the apparent magnitude that the telescope can see?

I have used the equation of

$5⋅log(\frac{D_1}{D_0})$
However, it gave the answer of 13.40, while the answer should be 19.40


texts: Can stars be seen in the background when looking directly at our solar system?

texts:
Imagine viewing the solar system from the outside:

Considering the sun is quite bright, would you still be able to see stars in the background, or does the sunlight disable us to do so?

Consider this photo:

Does the light from the sun disable us from seeing stars in the background or have they simply been removed in an editor after the fact of being taken (the photo)?

Obviously there needs be some way of seeing stars from space, since looking at photos from space stations (or even from Earth) those are full of stars.

But, viewing the solar system from above (from the outside), can you see stars in the background or does the sunlight simply block them out?


texts: What is the probability of an astronomical body hitting you?

texts:
It appears that there is already a calculated ballpark for meteor fatalities, but what about other factors such as space trash, comets, and other miscellaneous items in space?

Is it possible to obtain a ballpark estimate?


texts: Does our galaxy moves through space? Or does it stay in a single location? If it does move, what causes it to move?


texts: Why do we expect Type Ia Supernovae to be brighter in a decelerating Universe than what has been observed?

texts:
This seminal review paper in the PNAS by Robert P. Kirshner (https://www.pnas.org/content/96/8/4224) says the following:

  If the universe had been decelerating—–in the way it would if it contained the closure density of matter, that is, if Ωm = 1—then the light emitted at redshift z = 0.5 by a SN Ia would not have traveled as far, compared with a situation where the universe had been coasting at a constant rate—characteristic of an empty universe, where Ωm = 0. For a universe with Ωm = 1, the flux from the distant supernova therefore would be ≈25% brighter. But the distant supernovae are not brighter than expected in a coasting universe, they are dimmer. For this to happen, the universe must be accelerating while the light from the supernova is in transit to our observatories.

I didn't understand this.

Why do we expect Type Ia Supernovae at a particular distance to be more or less brighter based on the matter density of the Universe?

In other words, why should the brightness of anything at a particular distance  depend on whether the Universe was accelerating or not?